Factors Associated with SARS-CoV-2 and Influenza A Positivity and In-Hospital Mortality Among Hospitalized Patients with Suspected Acute Respiratory Infection: A Retrospective Cohort Study

Respiratory viral infections, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza A virus (IAV), represent a common cause of hospitalization among older adults and individuals with comorbidities. This retrospective cohort study, based on prospectively collected surveillance data, aimed to examine the epidemiological and clinical characteristics of hospitalized patients and identify predictors of SARS-CoV-2 and IAV positivity, as well as in-hospital mortality. The study included 832 patients hospitalized at the Military Medical Academy, a tertiary healthcare institution in Belgrade, and tested for respiratory viruses due to symptoms of acute respiratory infection (ARI) between 12 October 2023 and 5 June 2025. Demographic and clinical characteristics, comorbidities, length of hospital stay, and in-hospital outcomes were analyzed using univariable and multivariable logistic regression. SARS-CoV-2 was confirmed in 72 patients (8.7%), whereas IAV was detected in 40 (4.8%). Older age and sore throat were independently associated with SARS-CoV-2 positivity, whereas cough, fatigue, and hypertension were independently associated with IAV positivity. In-hospital mortality was 18.4%. Neither SARS-CoV-2 nor IAV positivity showed a statistically significant association with in-hospital mortality, although the limited numbers of virus-positive patients preclude firm conclusions. Given the overlap in clinical presentation, laboratory testing remains essential for etiological diagnosis, while recognition of these clinical factors may support risk stratification at the time of respiratory virus testing and closer patient monitoring.